Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-09-05
2003-04-22
Mai, Huy (Department: 2873)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S092000
Reexamination Certificate
active
06550981
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module. In particular, it relates an optical module having an optical coupling between an optical fiber and a laser diode.
2. Description of the Related Art
In a conventional optical module using a passive alignment mounting technique, it is important to ensure accuracy of the relative positions of a laser diode (LD) chip and an optical fiber at a sub-micron level.
Conventionally, therefore, a V-shape groove
17
(it may be simply called a V groove in this optical technology fields) is formed on a silicon (Si) substrate using anisotropic etching, and a mount mark (not shown) for mounting an LD chip
16
and a slit part
18
are also formed on the Si substrate
15
as shown in FIG.
1
. In
FIG. 1
, an optical fiber
20
is inserted into a ferrule
19
.
Referring to
FIGS. 2 and 3
, the LD chip
16
is mounted in alignment with the mount mark, and a portion of the optical fiber
20
is so mounted onto the V-shape groove
17
as to provide optical coupling with the LD chip
16
.
However, in the conventional optical module, while the mounting accuracy of the LD chip
16
on the Si substrate
15
is satisfactory, there is a problem in the mounting of the optical fiber
20
onto the V-shape groove
17
due to a high degree of flexibility of the optical fiber
20
.
More specifically, as shown in
FIG. 3
, since the end of the optical fiber
20
is likely to warp at the slit part
18
, it is rather difficult to mount the optical fiber
20
onto the V-shape groove
17
in a consistent state.
Moreover, in common practice of securing the optical fiber
20
to the V-shape groove
17
, the optical fiber
20
is temporarily set to the V-shape groove
17
first, and then a downward pressure is applied to the optical fiber
20
on the bevel of the V-shape groove
17
for positioning the optical fiber
20
.
At this process, if the V-shape groove
17
has any slight distortion, it is not allowed to accurately secure the optical fiber
20
at a predetermined position, i.e., accuracy of relative positions of the LD chip
16
and the optical fiber
20
cannot be attained at a sub-micron level, making it impossible to provide desired efficiency of optical coupling.
Even if the V-shape groove
17
is accurately formed, an end position of the optical fiber
20
may slightly vary depending on a pressing position to be taken or a degree of force to be exerted on the optical fiber
20
which has been temporarily set on the V-shape groove
17
, making it difficult to consistently secure the end of the optical fiber
20
at a predetermined accurate position.
Further, in positioning the optical fiber
20
for optical coupling between the LD chip
16
and the optical fiber
20
, the end position of the optical fiber
20
in relative relationship with the LD chip
16
is of critical importance. In the conventional technique of directly mounting the optical fiber
20
on the V-shape groove
17
, it is difficult to accurately determine the end position of the optical fiber
20
, giving rise to a significant problem in terms of workability and yield of optical coupling.
In Japanese Unexamined Patent Publication No. Hei-10-300987, there is disclosed a structure in which a ferrule
23
fixedly attached around an optical fiber
25
is used for optical coupling between an LD chip
22
mounted on an Si substrate
21
and the optical fiber
25
as shown in
FIGS. 4 and 5
.
In this conventional optical module, the ferrule
23
, which is made of zirconia, is fixedly attached around the optical fiber
25
, and then the ferrule
23
is directly mounted on the Si substrate
21
for providing optical coupling with the LD chip
22
. There is no groove formed on the Si substrate
21
, on the other hand, a notch part
24
is formed at the end of the ferrule
23
. A space between the LD chip
22
and the ferrule
23
is filled with a refractive index matching material
26
.
According to the conventional optical module, since the zirconia ferrule
23
which is sufficiently lower in flexibility than the optical fiber
25
is mounted on the Si substrate
21
, it is possible to enhance workability and stability with respect to a mounting position on the Si substrate
21
.
In the conventional optical module, however, since the notch part
24
is formed at the end of the zirconia ferrule
23
, there arises a problem of a substantial increase in fabrication cost of the ferrule
23
.
More specifically, it is rather difficult to form the notch part
24
because of poor working property of zirconia. For use in practice, the side face of the ferrule
23
must be finished with high precision. Since it is required to perform a process step of forming the notch part
24
before a process step of polishing the side face of the ferrule
23
, complexity occurs in fabrication of the ferrule
23
. In addition, it becomes difficult to handle the ferrule
23
having the notch part
24
formed thereon.
Further, when mounting the ferrule
23
on the Si substrate
21
, it is required to let the notch part
24
of the ferrule
23
meet a flat surface area of the Si substrate
21
. Therefore, the ferrule
23
must be adjusted properly in a rotational direction at the time of mounting, whereby the mounting process becomes more complex.
Moreover, though accuracy is required in formation of the notch part
24
at a sub-micron level, it is extremely difficult to ensure such high accuracy in fabrication of the ferrule
23
made of zirconia having poor working property. Still further, in this conventional optical module, a crosswise position reference is not available since no V-shape groove is formed on the Si substrate
21
. Therefore, it is impossible to attain crosswise positioning accuracy as high as that in the use of a V-shape groove.
Contrary to intended improvement in workability of mounting on the Si substrate
21
, the above problem would cause a decrease in mounting accuracy and an increase in fabrication cost.
Further, another conventional optical module is disclosed in Japanese Unexamined Patent Publication No. Hei 9-105839, wherein it has been proposed to provide a structure in which an optical fiber fixed in a stepped ferrule is set to a V-shape groove formed on an Si substrate and then an LD chip is securely positioned with high accuracy at the end of the stepped ferrule. According to this conventional optical module, it is possible to carry out the assembling and fixing of an optical fiber easily in a simple manner.
However, in this conventional optical module, since the ferrule has a stepped form, a thick-diameter part of the ferrule, which is coupled with an external optical connector, and a thin-diameter part of the ferrule, which is mounted on the V-shape groove, must be formed so that both of them are aligned with respect to center axes of the optical fiber and the ferrule.
Therefore, complexity occurs in fabrication of the ferrule, which would cause a substantial increase in fabrication cost and a decrease in yield.
The stepped structure of the ferrule in this conventional optical module is intended to prevent a stress from being applied to a retention part on the V-shape groove when a spring force is exerted from an external connector. In other words, since a stress is likely to concentrate at a stepped part of the ferrule, there is a possibility that the stepped ferrule may be damaged by a spring force exerted from the external connector.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical module and a method of making thereof capable of enhancing mounting accuracy of a ferrule.
Another object of the present invention is to provide an optical module and a method of making thereof capable of enhancing yield in making an optical module.
Still another object of the present invention is to provide an optical module and a method of making thereof capable of reducing fabrication cost.
In order to achieve the above objects, an optical module according to an embodiment of the present invention com
Mai Huy
NEC Corporation
Sughrue & Mion, PLLC
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